The invention relates to a projection exposure system, in particular for microlithography, for generating, in an image plane, an image of a mask arranged in an object plane, with a light source emitting projection light and projection optics arranged between the mask and the image, wherein the following are arranged in the beam path of the projection optics, starting from the mask:                a) a first group of optical components with an overall positive refractive power;        b) a second group of optical components with an overall negative refractive power;        c) a third group of optical components with an overall positive refractive power;        d) a fourth group of optical components with an overall negative refractive power and        e) a fifth group of optical components with an overall positive refractive power.        
Such projection optics are known from U.S. Pat. No. 6,349,005 B1 and U.S. Pub. No. 2003/1498551 A1 in the name of the Applicant. They are suitable, in particular, for use with projection light wavelengths in the DUV wavelength range. Instead of the fifth group of optical components with an overall positive refractive power, these documents also refer in places to a fifth and a sixth group of optical components, although these may be combined as a fifth group of optical components with an overall positive refractive power for the purposes of the invention described below.
Owing to the very high numerical aperture which projection optics of this type generally have, residual imaging errors occur, for example because of changes in the ambient parameters such as temperature and air pressure.
It is therefore an object of the present invention to provide projection optics for a projection exposure system of the type mentioned in the introduction, whose residual imaging errors are reduced.
This object is achieved according to the invention by the fact that                f) at least three (first, second and third) optical subgroups having at least one optical component can be displaced along the optical axis of the projection optics,        wherein        g) the first optical subgroup comprises the mask and at least one optical component from the first group of optical components,        h) the second optical subgroup comprises at least one optical component from the second or the third group of optical components,        i) the third optical subgroup comprises at least one optical component from the third or the fourth group of optical components.        
According the invention, it has been discovered that if at least three optical subgroups according to the above selection are chosen as instruments, which can be displaced along the optical axis, for correction of imaging errors of the projection optics, then good correction is ensured for the imaging errors which typically occur, for example scaling, distortion and image field curvature. In this case, the individual subgroups need not act selectively on one imaging error in each case, but rather it is sufficient for the combination of the actions of the three subgroups to bring about the desired correction effect. The optimum adjustment of the respective subgroups can be determined with the aid of known optical design programs.
Preferably, the second optical subgroup is arranged next to the first group of optical components. In this case, at least two displaceable subgroups are present in spatial proximity, which offers the possibility of simplifying the design of the projection optics.
The third optical subgroup may be arranged in the transition region between the third and the fourth groups of optical components. For most designs of projection optics of the type mentioned in the introduction, good correction of imaging errors which typically occur is obtained in this case.
A pair of optical components, whose displacements along the optical axis are expediently coupled together, may be provided as the second optical subgroup. Such a component pair has been found to be efficient in terms of optical corrective action, as has been shown by optical calculations.
Preferably, a support body is in this case provided, which can be displaced along the optical axis of the projection optics and which supports the two optical components together. This permits a simple mechanical structure for the optical components which can be displaced together.
An instrument for adjusting the wavelength may additionally be provided. According to the invention, it has been established that an instrument for adjusting the wavelength can in many cases fulfill the corrective function of an additional displaceable subgroup of optical components. In most cases, the wavelength adjustment means is easier to produce than an additional displaceable subgroup.
Preferably, the adjustment instrument includes means for altering the emission wavelength of the light source. Such an adjustment instrument is energy-efficient.
As an alternative or in addition, the adjustment instrument may include means for altering the projection light wavelength after exiting the light source. Such an adjustment instrument is easy to produce, for example by means of colour filters.
In a preferred refinement, at least a fourth optical subgroup, having at least one optical component, is provided which can be displaced along the optical axis and which comprises at least one optical component from the fifth group of optical components. With such an additional optical subgroup, it is possible to reduce other imaging errors which typically occur, such as coma and spherical aberration.
The at least a forth optical subgroup may comprise an at most fourth and a fifth optical subgroup. With comparatively minor mechanical outlay, such an embodiment provides good reduction of imaging errors which occur, as has been shown by optical calculations.
The optical components may be designed as refractive components. With refractive optical components, it is possible to produce projection optics of the type mentioned in the introduction with comparatively minor mechanical outlay. As an alternative, however, it is likewise possible to embody the projection optics with reflective components.